Exodus 27:21

As Yahweh commanded Moses, so Aaron placed it before the Testimony to be kept.

“They shall be on Aaron and on his sons when they come into the tent of meeting or when they approach the altar to minister in the holy place, so that they do not incur guilt and die. It shall be a perpetual statute to him and to his seed after him.

“Command the sons of Israel that they bring to you clear oil from beaten olives for the light, to make a lamp burn continually.

“So you shall keep the responsibility of the sanctuary and the responsibility of the altar, so that there will no longer be wrath on the sons of Israel.